As an optical device capable of changing refractive power of a lens, for example, a liquid crystal optical device having a structure in which a liquid crystal layer is arranged between a pair of transparent substrates having transparent electrodes is proposed as shown in FIG. 2 of JP-A-2001-133928 (Patent Document 1). In the liquid crystal optical device having the structure, refractive power of the lens can be changed by controlling a retardation distribution in the liquid crystal layer by changing a voltage between the pair of substrates.
In the liquid crystal optical device in which the lens is formed by smoothly changing the retardation distribution in the liquid crystal layer, the thickness of the liquid crystal layer have to be set to be considerably thicker than a liquid crystal layer in a normal liquid crystal display panel because an optical lens is formed. Therefore, response speed of the liquid crystal layer is reduced.
In a normal optical lens, the thickness can be reduced by applying a so-called Fresnel lens having a saw-tooth cross section. Also in the liquid crystal optical device, the Fresnel lens is formed by changing the retardation distribution in the liquid crystal layer in respective given areas to be a saw-tooth distribution, thereby allowing the thickness of the liquid crystal layer to be set thinner and increasing the response speed.